This in-game event takes place in Cyrodiil, Imperial City, and Battlegrounds. Therefore, it should be no surprise that this is a PvP event. You’ll have until February 9 until 10a ET to take place if you’re interested.
Rewards include double XP, Alliance points, plus collectibles specific to the event, including Achievements, and titles. If you want to participate, go to the Crown Store and grab the Details on the Midyear Mayhem quest. You can then go to your Alliance War’s faction in Cyrodiil. You can use the Alliance War menu. Keep in mind, you don’t have to travel to Cyrodiil to actually kick off the event.
Once you’re there, look for the NPC named Predicant Maera. Note, if you finished this quest last year, you won’t have to speak to the NPC again. Once you complete the quest, grab the Scroll of Pelinal’s Ferocity, plus a Pelinal Midyear Boon Box.
If you use the scrolls, you’ll receive a two hour 100% buff in Alliance War, Imperial City, and Battlegrounds. These will provide buffs to Alliance Points earned, and XP gains in PvP when you kill other players.